DE102019202029B4 - Process for producing a rubber base mixture and its use - Google Patents

Abstract

Process for producing a rubber base mixture containing at least one diene polymer, at least plasticizer oil and/or plasticizer resin and more than 80 phr filler in an internal mixer, wherein- a rubber mixture reduced in or free of plasticizer oil and/or plasticizer resin and reduced in or free of filler is produced in the internal mixer,- at least plasticizer oil and/or liquefied plasticizer resin and the remaining filler are mixed separately in a mixing device for fluids to form a filler-plasticizer precursor- and then this filler-plasticizer precursor is added to the rubber mixture in the internal mixer and mixed in, and wherein the remaining filler is silica and the ratio of silica to plasticizer oil and/or liquefied plasticizer resin during premixing is 1:0.4 to 1:3.

Description

The invention relates to a process for producing a rubber base mixture containing at least diene polymers, plasticizer oil and/or plasticizer resin and more than 80 phr of filler in an internal mixer. The invention further relates to the use of such a rubber base mixture for producing vehicle tires.

Rubber mixtures are usually produced in such a way that a base mixture with all components (accompanying chemicals) except the vulcanization system (sulfur and substances that affect vulcanization) is first produced in one or more mixing stages. The finished mixture is produced by adding the vulcanization system in a final mixing stage. The finished mixture is further processed, for example, by an extrusion process and brought into the appropriate shape. Further processing then takes place by vulcanization. Internal mixers (kneaders) are generally used to produce the base rubber mixtures.

An alternative process for producing a rubber mixture is disclosed by DE 10 2015 225 985 A1 in which a low-viscosity premix is produced from a low-viscosity rubber component and filler and this premix is then mixed with a higher-viscosity rubber premix.

Nowadays, a large number of rubber mixtures are produced with a high proportion of fillers. On the one hand, the fillers help to make the mixtures cheaper, and on the other hand, they have a decisive influence on the various material properties of the mixture and the resulting vulcanizate. The fillers that can be used in rubber mixtures include carbon black, silica, aluminosilicates, chalk, starch, magnesium oxide, titanium dioxide or rubber gels as well as carbon nanotubes, graphite and graphene and so-called "carbon-silica dual-phase fillers".

In order to reduce the rolling resistance of pneumatic vehicle tires, it has long been known to use silica as a filler, even in larger quantities, for the rubber compound of the tread.

If the proportion of filler is increased in rubber mixtures, the associated hardening of the rubber must be counteracted by adding plasticizer oil or plasticizer resin in order to achieve a specified hardness. Examples of plasticizer oils that can be used are aromatic, naphthenic or paraffinic mineral oil plasticizers, such as MES (mild extraction solvate) or RAE (residual aromatic extract) or TDAE (treated distillate aromatic extract), or rubber-to-liquid oils (RTL) or biomass-to-liquid oils (BTL), as well as vegetable oils such as rapeseed oil and liquid polymers.

Large amounts of filler are difficult to incorporate in an internal mixer in one mixing step. If the filler is silica, silane coupling agents are often added to these basic mixtures to bind the silica to the surrounding polymers. This also creates the problem that when silica reacts with the silane coupling agent (silanization reaction), alcohol is released, which can lead to flammable mixtures in the mixer or in the mixer shaft.

The invention is based on the object of providing a process for producing a rubber base mixture which allows the simple introduction of large amounts of filler without negatively affecting the properties of the vulcanizates from the mixture.

• - eine um Weichmacheröl und/oder Weichmacherharz reduzierte oder von diesen freie und um Füllstoff reduzierte oder von diesem freie Kautschukmischung im Innenmischer erstellt wird,
• - separat in einer Mischvorrichtung für Fluide zumindest Weichmacheröl und/oder verflüssigtes Weichmacherharz und der restliche Füllstoff zu einem Füllstoff-Weichmacher-Vorprodukt vermischt werden
• - und im Anschluss dieses Füllstoff-Weichmacher-Vorprodukt in den Innenmischer zu der Kautschukmischung gegeben und eingemischt wird und
• - wobei der restliche Füllstoff Kieselsäure ist und das Verhältnis von Kieselsäure zu Weichmacheröl und/oder verflüssigtem Weichmacherharz beim Vorvermischen 1:0,4 bis 1:3 beträgt.

This task is solved by the fact that in the method of the type mentioned above

• - a rubber mixture reduced in or free of plasticizer oil and/or plasticizer resin and reduced in or free of filler is produced in the internal mixer,
• - at least plasticizer oil and/or liquefied plasticizer resin and the remaining filler are mixed separately in a mixing device for fluids to form a filler-plasticizer precursor
• - and then this filler-plasticizer precursor is added to the rubber mixture in the internal mixer and mixed in and
• - where the remaining filler is silica and the ratio of silica to plasticizer oil and/or liquefied plasticizer resin during premixing is 1:0.4 to 1:3.

By creating a filler-plasticizer precursor from plasticizer oil and/or liquefied plasticizer resin and filler, it is possible to mix even large amounts of filler evenly into a rubber mixture. This is possible without increasing the amounts of plasticizer for the desired target hardness of a mixture. The amount of plasticizer in the resulting (final) base mixture can remain unchanged compared to a conventionally produced mixture. The vulcanizate properties are not negatively affected by this. In addition, the process according to the invention offers the advantage that the amount of air trapped in the filler and thus introduced into the rubber mixture can be significantly reduced. The amount of free plasticizer not on the filler or unwetted filler is reduced in the process according to the invention compared to a conventional process for producing a base mixture. If the filler is used in granulate form, a large proportion of its internal hollow structure is filled with plasticizer. In the event that the plasticizer has already been mixed with other chemicals, such as e.g. B. a silane coupling agent, the inner surface of the filler also becomes accessible to other chemicals, such as silane coupling agents. This enables chemical reactions, such as the silanization reaction, to be carried out in the precursor production.

In the case of the rubber mixture in the internal mixer with reduced filler, the reduction of the filler can be reduced to a quantity of 0 phr. However, it is advantageous if at least 20 phr of filler is mixed into the rubber mixture in the internal mixer in the first step. The phr (parts per hundred parts of rubber by weight) used in this document is the quantity specification for mixture recipes commonly used in the rubber industry. The dosage of the parts by weight of the individual substances is always based on 100 parts by weight of the total mass of all rubbers present in the mixture. The mass of all rubbers present in the mixture adds up to 100.

The mixing device for fluids can be a simple stirring device, but preferably a fluid mixer is used.

The rubber base mixture produced by the process according to the invention contains at least one diene polymer. Several diene polymers can also be used in a blend. Diene rubbers include all rubbers with an unsaturated carbon chain that are at least partially derived from conjugated dienes.

The rubber base mixture can contain polyisoprene (IR, NR) as diene rubber. This can be either cis-1,4-polyisoprene or 3,4-polyisoprene. However, the use of cis-1,4-polyisoprenes with a cis-1,4 content of > 90 wt.% is preferred. On the one hand, such a polyisoprene can be obtained by stereospecific polymerization in solution with Ziegler-Natta catalysts or using finely divided lithium alkyls. On the other hand, natural rubber (NR) is such a cis-1,4 polyisoprene, the cis-1,4 content in natural rubber is greater than 99 wt.%. Natural rubber (NR) is understood to mean rubber that can be obtained by harvesting from sources such as rubber trees (Hevea brasiliensis) or non-rubber tree sources (such as guayule or dandelion (e.g. Taraxagum koksaghyz)).

If the rubber base mixture contains polybutadiene (BR) as diene rubber, it can be cis-1,4-polybutadiene. The use of cis-1,4-polybutadiene with a cis-1,4 content of more than 90% by weight is preferred, which can be produced, for example, by solution polymerization in the presence of rare earth catalysts.

Other diene rubbers that can be used are vinyl-polybutadienes and styrene-butadiene copolymers. The vinyl-polybutadienes and styrene-butadiene copolymers can be solution-polymerized (styrene)-butadiene copolymers (S-(S)BR) with a styrene content, based on the polymer, of approximately 0 to 45% by weight and a vinyl content (content of 1,2-bonded butadiene, based on the total polymer) of 10 to 90% by weight, which can be produced, for example, using lithium alkyls in an organic solvent. The S-(S)BR can also be coupled and end-group modified. However, emulsion-polymerized styrene-butadiene copolymers (E-SBR) and mixtures of E-SBR and S-(S)BR can also be used. The styrene content of the E-SBR is approximately 15 to 50 wt.% and the types known from the prior art obtained by copolymerization of styrene and 1,3-butadiene in aqueous emulsion can be used.

The diene rubbers used in the mixture, in particular the styrene-butadiene copolymers, can also be used in partially or fully functionalized form. The functionalization can be carried out with groups that are compatible with the fillers used, in particular with OH groups. fillers. This can be, for example, functionalization with hydroxyl groups and/or epoxy groups and/or siloxane groups and/or amino groups and/or phthalocyanine groups and/or carboxy groups and/or silane sulfide groups. The diene rubbers can also be coupled additionally or alternatively.

In addition to the diene rubbers mentioned, the mixture can also contain other types of rubber, such as styrene-isoprene-butadiene terpolymer, butyl rubber, halobutyl rubber or ethylene-propylene-diene rubber (EPDM).

The rubber base mixture produced by the process according to the invention contains plasticizer oil and/or plasticizer resin. These can be different types in different amounts. Several types of plasticizer oils and plasticizer resins can also be present at the same time. Examples of plasticizer oils that can be used are aromatic, naphthenic or paraffinic mineral oil plasticizers, such as MES (mild extraction solvate) or RAE (residual aromatic extract) or TDAE (treated distillate aromatic extract), or rubber-to-liquid oils (RTL) or biomass-to-liquid oils (BTL), as well as vegetable oils such as rapeseed oil and liquid polymers. Plasticizer resins that can be used are those that melt at a temperature of up to 140 °C and can be absorbed by the filler in liquefied form.

According to an advantageous development of the invention, plasticizer oil and/or liquefied plasticizer resin are preheated before being introduced into the mixing device for fluids. In this way, these substances can be mixed more quickly with the filler and reach the pores of the filler.

The rubber base mixture contains more than 80 phr of filler. The rubber base mixture preferably contains 95 to 250 phr of filler. The process according to the invention has proven to be particularly advantageous for such highly filled rubber mixtures.

The filler can be a wide variety of materials, which can be used individually or as mixtures. The fillers that can be used in rubber mixtures include carbon black, silica, aluminosilicates, chalk, starch, magnesium oxide, titanium dioxide or rubber gels as well as carbon nanotubes, graphite and graphene and so-called "carbon-silica dual-phase fillers". The base mixture produced using the process can contain carbon black and silica in different quantities. The fillers can be used as different types, for example with different active surfaces. The fillers can be used in the form of granules or powder, for example.

The ratio of filler to plasticizer oil and/or liquefied plasticizer resin during premixing is preferably set so that the addition of the precursor changes the hardness (Shore A at room temperature) of the rubber base mixture, if this were produced without the process according to the invention with the addition of the filler-plasticizer precursor, by less than 5 hardness points. A ratio of filler to plasticizer oil and/or liquefied plasticizer resin that changes the hardness (Shore A at room temperature) of the rubber base mixture by less than 2 hardness points is particularly preferred.

When using pearlized fillers, it is also advantageous if a ratio of filler to plasticizer oil and/or liquefied plasticizer resin is set during premixing, in which the pearling state of the filler is maintained. Such a filler-plasticizer precursor can be easily dosed and added using the dosing systems customary for fillers.

The remaining filler, which is mixed in a fluid mixing device to form the filler-plasticizer precursor, is silica. Silica is particularly difficult to mix in large quantities into rubber compounds without causing mixing problems.

To ensure good mixing of silica and plasticizer oil or liquefied plasticizer resin and problem-free mixing of the filler-plasticizer precursor into the rest of the rubber mixture, the ratio of silica to plasticizer oil and/or liquefied plasticizer resin during premixing is 1:0.4 to 1:3.

If the rubber mixture contains silica, silane coupling agents can be added to the mixture to improve processability and to bind the polar filler to the rubber. The silane coupling agents react with the surface silanol groups of the silica or other polar groups during mixing of the rubber or rubber mixture (in situ) or before the filler is added to the rubber in the sense of pretreatment (premodification). All silane coupling agents known to the person skilled in the art for use in rubber mixtures can be used as silane coupling agents. Such coupling agents known from the prior art are bifunctional organosilanes which have at least one alkoxy, cycloalkoxy or phenoxy group as a leaving group on the silicon atom and which have as another functionality a group which can enter into a chemical reaction with the double bonds of the polymer after cleavage. The latter group can, for example, be the following chemical groups: -SCN, -SH, -NH ₂ or -S _x - (where x = 2-8). Thus, 3-mercaptopropyltriethoxysilane, 3-thiocyanatopropyltrimethoxysilane or 3,3'-bis(triethoxysilylpropyl)polysulfides with 2 to 8 sulfur atoms, such as 3,3'-bis(triethoxysilylpropyl)tetrasulfide (TESPT), the corresponding disulfide or mixtures of the sulfides with 1 to 8 sulfur atoms with different contents of the various sulfides, can be used as silane coupling agents. The silane coupling agents can also be added as a mixture with industrial carbon black, such as TESPT on carbon black (trade name X50S® from Evonik). Blocked mercaptosilanes, such as those from WO 99/09036 can be used as silane coupling agents. Silanes, such as those used in WO 2008/083241 A1 , the WO 2008/083242 A1 , the WO 2008/083243 A1 and the WO 2008/083244 A1 can be used. Silanes that can be used are, for example, those sold under the name NXT® in various variants by Momentive, USA, or those sold under the name VP Si 363® by Evonik Industries. So-called “silated core polysulfides” (SCP, polysulfides with a silylated core) can also be used, which are used, for example, in the US 20080161477 A1 and the EP 2 114 961 B1 be described.

According to an advantageous development of the invention, a silane coupling agent is added in the process during the production of the filler-plasticizer precursor from plasticizer oil and/or liquefied plasticizer resin and silica. This allows at least a partial bonding (hydrophobization) of the silane coupling agent to the silica to take place in a preceding step.

The alcohol produced during this reaction can escape and be collected before it is mixed into the rest of the rubber mixture and no longer causes problems in the internal mixer or mixer shaft due to the possible formation of flammable mixtures.

In order to carry out the hydrophobization reaction between silica and silane coupling agent as far as possible and to remove the resulting alcohol as completely as possible before mixing the filler-plasticizer precursor into the remaining rubber mixture, it is preferred if the filler-plasticizer precursor is produced at a temperature of more than 80 °C, preferably more than 120 °C.

In addition to the substances already mentioned, the rubber base mixture can contain other additives that are common in the rubber industry in the usual parts by weight. These additives include, for example, anti-aging agents such as N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (6PPD), N-isopropyl-N'-phenyl-p-phenylenediamine (IPPD), 2,2,4-trimethyl-1,2-dihydroquinoline (TMQ) and other substances such as those from J. Schnetger, Lexicon of Rubber Technology, 2nd edition, Hüthig Buch Verlag, Heidelberg, 1991, pp. 42-48 known, activators such as zinc oxide and fatty acids (e.g. stearic acid), waxes, adhesive resins such as hydrocarbon resins and rosin, and mastication aids such as 2,2'-dibenzamidodiphenyl disulfide (DBD).

The rubber base mixture produced by the process according to the invention is usually further processed into a finished mixture. For this purpose, vulcanization chemicals such as sulfur, sulfur donors or peroxides and substances that influence vulcanization such as vulcanization accelerators, vulcanization retarders and vulcanization activators are mixed in.

The rubber base mixture produced by the process according to the invention can be used in a wide variety of products. These products include rubber bellows, conveyor belts, air springs, belts, straps, hoses, printing blankets, vibration metals or shoe soles. However, the rubber base mixture produced by the process according to the invention is preferably used for the production of of vehicle tires, since large amounts of filler are often mixed into rubber base compounds for vehicle tires.

The invention will now be explained in more detail using exemplary embodiments in conjunction with the tables below. The comparison mixtures are marked with Ref. or V, the mixtures produced according to the invention are marked with E. In the tables, the Shore A hardness at room temperature was measured using a durometer in accordance with DIN ISO 7619-1 and the rebound resilience at room temperature in accordance with DIN 53 512. Table 1: Silica mixture with TESPD components Unit Ref. 1 Ref. 2 E1 E2 diene polymer phr 100 100 100 100 silica ^a phr 120 70 70 70 plasticizer oil ^b phr 50 0 0 0 Silane coupling agent ^c Filler-plasticizer precursor with silane phr 9 5 5 5 coupling agent phr 0 0 52 104 anti-aging agents phr 2 2 2 2 zinc oxide phr 2 2 2 2 stearic acid phr 1 1 1 1 process aids phr 2 2 2 2 sulfur cross-linking system phr 5 4 4.5 5 material properties hardness at RT Shore A 70 70 70 70 rebound resilience at RT % 23 40 30 23 ^a) Ultrasil ^® VN3, Evonik company ^b) MES oil ^c) TESPD, bis(3-triethoxysilylpropyl) disulfide

Four rubber base mixtures were produced in an internal mixer according to Table 1. In reference mixture 1, 120 phr of silica was mixed in, which required a long mixing time with several additions of silica in order to achieve the most homogeneous distribution of silica in the mixture.

In the mixtures in Table 1, which were mixed according to the process according to the invention, a filler-plasticizer precursor with silane coupling agent was first produced in a fluid mixer from 48 parts by weight of plasticizer oil, 48 parts by weight of silica and 4 parts by weight of silane coupling agent. This filler-plasticizer precursor was then added to the other mixture components in the internal mixer during the production of the rubber base mixture. The amounts of pure silica, silane coupling agent and pure plasticizer oil were reduced accordingly in the precursor stage so that the resulting rubber base mixtures contained 95 and 120 phr of silica, respectively. These rubber base mixtures were significantly easier to produce and process than the reference mixtures. The silica could be mixed in homogeneously in a short time.

The rubber base mixtures were then processed into finished mixtures and used in the manufacture of pneumatic vehicle tires. No differences in the vulcanizate properties could be determined. For mixtures E1 and E2, the vulcanizates had the same hardness despite different amounts of precursor. Table 2: Silica mixture with blocked mercaptosilane components Unit Ref. 3 Ref. 4 E3 E4 diene polymer phr 100 100 100 100 silica ^a phr 120 70 70 70 plasticizer oil ^b phr 50 0 0 0 Silane coupling agent ^c Filler-plasticizer precursor with silane phr 10 6 6 6 coupling agent phr 0 0 52 104 anti-aging agents phr 2 2 2 2 zinc oxide phr 2 2 2 2 stearic acid phr 1 1 1 1 process aids phr 2 2 2 2 sulfur cross-linking system phr 5 3 4 5 material properties hardness at RT Shore A 65 65 65 65 rebound resilience at RT % 28 42 34 28 ^a) Ultrasil ^® VN3, Evonik company ^b) MES oil ^c) blocked mercaptosilane, NXT® silane from Momentive

Four rubber base mixtures were produced in an internal mixer according to Table 2. In reference mixture 3, 120 phr of silica was mixed in, which required a long mixing time with several additions of silica in order to achieve the most homogeneous distribution of silica in the mixture.

In the mixtures in Table 2, which were mixed according to the process according to the invention, a filler-plasticizer precursor with silane coupling agent was first produced in a fluid mixer from 48 parts by weight of plasticizer oil, 48 parts by weight of silica and 4 parts by weight of silane coupling agent. This filler-plasticizer precursor was then added to the other mixture components in the internal mixer during the production of the rubber base mixture. The amounts of pure silica, silane coupling agent and pure plasticizer oil were reduced accordingly in the precursor stage so that the resulting rubber base mixtures contained 95 and 120 phr of silica, respectively. These rubber base mixtures were significantly easier to produce and process than the reference mixtures. The silica could be mixed in homogeneously in a short time.

The rubber base mixtures were then processed into finished mixtures and used in the manufacture of pneumatic vehicle tires. No differences in the vulcanizate properties could be determined. For mixtures E3 and E4, the vulcanizates had the same hardness despite different amounts of precursor. Table 3: Carbon black mixture components Unit Ref. 5 Ref. 6 V1 V2 diene polymer phr 100 100 100 100 soot ^a phr 120 70 70 70 plasticizer oil ^b phr 50 0 0 0 filler-plasticizer precursor phr 0 0 50 100 anti-aging agents phr 2 2 2 2 zinc oxide phr 2 2 2 2 stearic acid phr 1 1 1 1 process aids phr 2 2 2 2 sulfur cross-linking system phr 3 3 3 3 material properties hardness at RT Shore A 73 73 73 73 rebound resilience at RT % 19 38 27 19 ^a) Soot N339 ^b) MES oil

Four rubber base mixtures were produced in an internal mixer according to Table 3. In reference mixture 5, 120 phr of carbon black was mixed in, which required a long mixing time with several additions of the carbon black in order to achieve the most homogeneous distribution of the carbon black in the mixture.

For the mixtures in Table 3, which were mixed using a different method, a filler-plasticizer precursor was first produced from 45 parts by weight of plasticizer oil and 55 parts by weight of carbon black in a fluid mixer. This filler-plasticizer precursor was then added to the other mixture components in the internal mixer during the production of the rubber base mixture. The amounts of carbon black and pure plasticizer oil were reduced accordingly in the precursor stage so that the resulting rubber base mixtures contained 97.5 and 125 phr of carbon black, respectively. These rubber base mixtures were significantly easier to produce and process than the reference mixtures. The carbon black could be mixed in homogeneously in a short time.

The rubber base mixtures were then further processed into finished mixtures and used in the manufacture of pneumatic vehicle tires. No differences in the vulcanizate properties could be determined. For mixtures V1 and V2, the vulcanizates had the same hardness despite different amounts of precursor.

Claims (5)

Process for producing a rubber base mixture containing at least one diene polymer, at least plasticizer oil and/or plasticizer resin and more than 80 phr filler in an internal mixer, whereby - a rubber mixture reduced in plasticizer oil and/or plasticizer resin or free of these and reduced in filler or free of this is produced in the internal mixer, - at least plasticizer oil and/or liquefied plasticizer resin and the remaining filler are mixed separately in a mixing device for fluids to form a filler-plasticizer precursor - and then this filler-plasticizer precursor is added to the rubber mixture in the internal mixer and mixed in, and whereby the remaining filler is silica and the ratio of silica to plasticizer oil and/or liquefied plasticizer resin during premixing is 1:0.4 to 1:3. Process for producing a rubber base mixture according to claim 1 , characterized in that plasticizer oil and/or liquefied plasticizer resin are preheated before being introduced into the mixing device for fluids. Process for producing a rubber base mixture according to at least one of the Claims 1 or 2 , characterized in that a silane coupling agent is added during the production of the filler-plasticizer precursor from plasticizer oil and/or liquefied plasticizer resin and silica. Process for producing a rubber base mixture according to claim 3 , characterized in that the production of the filler-plasticizer precursor takes place at a temperature of more than 80 °C, preferably more than 120 °C. Use of the data obtained in accordance with the procedures claim 1 until 4 manufactured rubber base compounds for the production of vehicle tires.